It is the nature of hydraulic trim presses and the like to require high approach speed in order to minimize cycle time as well as high pressure at the end of the stroke to cut through the material being trimmed, pierced or pressed. In order to meet the foregoing requirements, elaborate hydraulic circuits have been developed in order to avoid the necessity of using oversized cylinders and increased oil flow rate. However, the elaborate hydraulic circuits, by necessity, require more complicated piping and valving arrangements which in turn are susceptible to increased incidence of oil leaks which in turn lead to excessive maintenance and down time.
The conventional trim press generally comprises a bed connected to a stationary platen by tie rods. A movable platen that is guided by the tie rods is actuated by a hydraulic cylinder mounted centrally of the stationary platen with the piston rod connected to the movable platen. The hydraulic cylinder is mounted above the stationary platen. Generally, there is an oil reservoir tank mounted near the hydraulic cylinder and in conventional presses it may surround the hydraulic cylinder or be positioned above the hydraulic cylinder or to one side of the hydraulic cylinder.
With the oil reservoir tank surrounding the cylinder, it naturally requires heavier steel material with the associated increase in cost. With the oil reservoir tank situated above the hydraulic cylinder, it increases the height of the press, thus making it undesirable in view of the increased height as well as being unstable. With the oil reservoir tank being mounted to one side of the hydraulic cylinder an inherent unstable situation is created and is therefore undesirable.
With the single hydraulic cylinder and piston system, as the piston is driven up and down, there is a great deal of bending moments created in the stationary platen due to the distance from the centre of the hydraulic piston to the extreme edges of the stationary platen, resulting in the need for the stationary platen to be of greater thickness. In other words, the maximum bending moment for the single hydraulic cylinder is the product of the full press tonnage acting at the centre of the longest span while the maximum bending moment for the present invention is the product of one-half of the tonnage acting at the centre of the shortest span.
Also with the single hydraulic cylinder and piston system, if the piston rod breaks it requires a separate safety system in order to prevent the press from falling down due to its own weight.
Further, with the single hydraulic cylinder and piston system it is not possible to put knock-out rods in the centre of the stationary platen.
It is, therefore, an object of the present invention to overcome the foregoing problems by providing a hydraulic trim press having two spaced apart hydraulic cylinder and piston system, a hydraulic tank for storage of hydraulic fluid attached to the underside of the stationary platen and located centrally thereof, and a solid metal manifold with holes drilled therethrough to conduct the hydraulic fluids to the control valves and cylinders in order to avoid the high pressure external hydraulic pipes as required in conventional presses as well as most other external pipes.